Potassium Bitartrate

potassium bitartrate

KHC4H4O6 White, water-soluble crystals or powder; used in baking powder, for medicine, and as an acid and buffer in foods. Also known as cream of tartar; potassium acid tartrate.

Potassium Bitartrate

(cream of tartar), the acid potassium salt of tartaric acid, a crystalline precipitate that settles with yeast during the alcoholic fermentation of grape must and in the subsequent storage and processing of the wine. Potassium bitartrate is also present in solution in grape juice. It forms a saturated solution in the wine. The precipitation of minute crystals can start in finished, bottled wine owing to mechanical jolts or a drop in temperature. To prevent this, the wine is kept at a temperature close to its freezing point before bottling. Potassium bitartrate is a valuable raw material for making tartaric acid. It is also used in tin electroplating, in dyeing cloth (as a mordant), and in baking bread.

Potassium bitartrate causes harmless clear crystals to form which can look alarmingly similar to tiny shards of glass.

Where cold chilling is not possible, potassium bitartrate crystallization can be inhibited by adding metatartaric acid as is commonly done in home winemaking but not allowed in commercial wines in many winemaking regions of the world.

The chemical equilibrium and kinetics of potassium bitartrate or "cold stability" in wine is not simple, and at least five issues must be considered whenever evaluating cellar or laboratory methods to understand if all known limiting factors have been addressed.

Tiburzi points out that tartrate crystal control is especially important for sparkling wines, because it is hard-edged surfaces--bottle imperfections, intentional imperfections in crystal glassware, or potassium bitartrate crystals--that serve as the launching pads for those wonderful streams of bubbles.

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